Steam pipes are used for a boiler and a steam turbine in a power plant. Steam for power flowing through such a steam pipe includes, for example, high-temperature and high-pressure steam at a temperature of 280° C. or more at a pressure of 6 Mpa or more. At a thermal power plant, steam of a higher temperature and a higher pressure tends to be used to improve power generation efficiency.
A pipe for high-temperature and high-pressure fluid, such as a steam pipe, is subjected to high temperature and high pressure over a long period of time, and accordingly is under creep fatigue caused by heat stress. In order to improve endurance under creep fatigue, high-chromium steel (chromium-molybdenum steel having a higher chromium content rate than common steel) such as 9Cr steel or 12Cr steel is used suitably for a pipe. This pipe is formed such that plate-like base members made of high-chromium steel are curved in a circular shape and such base members are integrated by welding. However, in a weld portion in high-chromium steel, damage, such as a crack, hardly occurs until the end stage of its life, resulting in difficulty in estimating its remaining life.
Then, in a method described in Patent Literature 1, such remaining life is estimated using creep ductility and creep strain. Further, a method described in Patent Literature 2, a constant in the Monkman-Grant analysis is obtained using a steel pipe specimen imitating a high-chromium steel pipe.